1. Field of the Invention
The present invention relates generally to an impedance matching system, a network analyzer having the same, and an impedance matching method thereof. More particularly, the present invention relates to an impedance matching system capable of more quickly and accurately matching an impedance of a load, a network analyzer having the same, and an impedance matching method thereof.
2. Description of the Related Art
Generally, in a load, such as an antenna, a value of load impedance for optimizing an output of the load is set up in advance. Generally, antennas are set up to have an impedance of 50Ω.
Accordingly, in order to maintain a performance of the load in an optimum condition, it is important for the impedance to be always maintained in the value set up in advance. However, the value of the impedance can be easily changed by an external environment, a linearity, etc. For instance, if a temperature or humidity is too high or low, and if there is a metal substance around the antenna, the value of the impedance is changed.
If the value of the impedance is changed as described above, during transmission of radio frequency (RF) signals, an electric power efficiency of RF signals, which are outputted through the antenna, is lowered. As a result, a portion of the RF signals to be transmitted is reflected from an input end side of the antenna to flow in a reverse direction, and is inputted into a transmitting circuit. Also, during reception of RF signals, an electric power efficiency of RF signals, which are received through the antenna, is lowered. As a result, RF signals are not received well, and the received RF signals flow in a reverse direction to be outputted through the antenna.
During the transmission and the reception of the RF signals, a phase difference and an amplitude ratio of the signals reflected from the antenna to the RF signals outputted through the antenna can be represented as a reflection coefficient. The reflection coefficient represents a degree in change of the impedance and a degree in performance deterioration of the antenna. The reflection coefficient comes to 0 in an ideal condition, that is, when there is no signal reflected into the transmitting circuit during the transmission of the RF signals and there is no signal outputted through the antenna during the reception of the RF signals. Accordingly, the reflection coefficient can be used as a standard of determining the impedance.
When the value of the impedance is changed as described above, to again match the impedance to 50Ω, there have been used various methods. Among the various methods, a method of matching the impedance using a matching circuit is mainly used.
Generally, the matching circuit is made up of elements including an inductor, a capacitor (or a condenser), etc. The capacitor is formed of a varactor in which a capacitance is varied according to a voltage. Accordingly, if a voltage, which is applied to the matching circuit, is varied, an inductance of the inductor and a capacitance of the condenser are varied, thereby enabling the impedance to be changed.
In case of using such a matching circuit, to accurately determine the voltage to be applied to the matching circuit is the key to accurately match the impedance. To determine the voltage, various methods are used.
In recent, with a minimization of a mobile phone, a size of the antenna is minimized, and/or the antenna is even built-in. However, the smaller the size of the antenna is, the more the matching of impedance is difficult in fabrication and is affected by the environment than in a normal size antenna in operation. Accordingly, if the conventional voltage determining method is used to a small size antenna, it is not only difficult to sufficiently and accurately match the impedance, but also necessary to repeat the impedance matching procedure several times to match the impedance. Thus, there is required a new method capable of more quickly and accurately carrying out the matching of impedance.